In commercial container filling or packaging operations, containers are moved by a conveyor or a conveying system at high rates of speed, up to 1000 containers per minute or more. In current bottling operations, copious amounts of lubricant solutions in dilute aqueous form (usually based on ethoxylated amines or fatty acid amines) are typically applied to the conveyor or containers using spray, fountain or other pumping equipment. Some aqueous conveyor lubricants are not compatible with thermoplastic beverage containers made of polyethylene terephthalate (PET) and other plastics. Conventional lubricants typically require use of large amounts of diluent water on the conveying line, which must then be disposed of or recycled, causing a wet environment.
The containers are filled with foods, water, carbonated or non-carbonated beverage in a filling apparatus that involves a moving conveyor surface that transports the container during filling. The conveyor structure comprises a filling or packing station, a capping station and often ends at a station for labeling or final storage. Initially such conveyor systems were lubricated using large amounts of lubricant diluted with large amounts of water. Representative examples of such aqueous conveyor lubricant compositions applied to conveyors are found in Stanton et al., U.S. Pat. No. 4,274,973 and Stanton, U.S. Pat. No. 4,604,220. A series of allegedly stress crack inhibiting substantially soluble aqueous lubricants were introduced including Rossio et al., U.S. Pat. Nos. 4,929,375 and 5,073,280; and Wieder et al., U.S. Pat. No. 5,009,801. These patents assert that certain substituted aromatic compounds, certain couplers and saponifying agents and certain amine compounds can inhibit stress cracking in appropriately formulated materials.
In large part the compositions used in these conventional systems are either clear solutions or suspensions (macroemulsions) of sparingly soluble materials in water. Many conventional systems are clear solutions of neutralized fatty acids in an aqueous base or solutions of soluble ethoxylated amines in an aqueous medium. However, conventional silicone emulsions are either opaque or translucent depending on concentration. Conventional silicone emulsions are macroemulsions of sparingly soluble or insoluble materials dispersed in an aqueous medium.
A substantial need exists for improved methods lubricating common container materials in any environment. Lubricant composition should provide an acceptable level of lubricity for the system. The lubricant preferably has a viscosity which allows it to be applied by conventional pumping and/or application apparatus, such as by spraying, roll coating, wet bed coating, and the like, commonly used in the industry.
We have found that current methods of lubricating such containers are wasteful of the lubricant material since a substantial proportion of the materials is lost as it leaves the container surface. Further, substantial proportions of the lubricant remain on the container as a foam and are carried from the conveyor as the food packaging or beverage-bottling operations are continued. Many available lubricant materials that have sparingly soluble or insoluble lubricant materials in an aqueous medium can separate and form a separate phase which, under certain circumstances, can be incompatible with operating systems. Such materials can plug lines, pumps and nozzles. Further, such lubricant materials often are not preferred by operating personnel for use in lubricating lines because of their hazy, translucent appearance or lack of clarity.
We have found that the properties of lubricants can be substantially improved if a substantially clear or transparent lubricant is formulated such that two separate, mutually insoluble hydrophilic and oleophilic phases are used in a formulation such that one phase is dispersed in another phase. The dispersion form is a thermodynamically stable composition. Preferred compositions are considered to be in the form of a microemulsion. The composition can be a oleophilic phase dispersed in a hydrophilic phase or a hydrophilic phase dispersed in an oleophilic phase. A preferred product format involves dispersing oleophilic materials into a hydrophilic phase. The oleophilic material can be common oils including natural oils, petroleum derived oils, silicone oils, or other oily or oleophilic material that can be dispersed in aqueous phase. The hydrophilic phase can comprise water, an aqueous solution or a water soluble, water miscible or aqueous compatible composition.
A microemulsion is a thermodynamically stable dispersion of one liquid phase in another phase, each phases being substantially insoluble in the other. An interfacial film of surfactant typically stabilizes a microemulsion. The microemulsion may be in the form of either an oil-in-water or water-in-oil composition. In oil-in-water forms, the oil is dispersed as very small droplets in continuous water or aqueous phase. In a water-in-oil microemulsion, water droplets are dispersed into an oil continuous phase. Microemulsions, different than a typical, opaque or translucent suspension, emulsion or macroemulsion, are typically clear compositions. The clarity of the solution results from the droplet size which is typically smaller than the smallest wavelength of a visible light radiation (about 350 nm). Since the particle size is smaller than light wavelengths, it is believed that the light is not scattered by the small droplets resulting in transparent solutions. The interfacial tension between the two phases are relatively low, adding to the thermodynamic stability of the microemulsion particles in the continuous phase. In substantial contrast to a microemulsion, a dispersion, emulsion (or macroemulsion) is an unstable suspension of droplets in a continuous phase. Such droplets will typically agglomerate, coalesce and, at some point, can separate from the continuous phase. In macroemulsions, the droplet sizes are much larger, typically 1 micron or more resulting in a cloudy or milky dispersion. The clear lubricants of the invention which we believe is a microemulsion may be applied to the conveyor without dilution or with a relatively modest dilution, e.g. at a water:lubricant ratio of less than 10:1 in a thin coating of lubricant formed by applying relatively small amounts of lubricant onto the moving container bearing surface of the conveyor. Alternatively, the microemulsion compositions of the invention can be diluted with water to form a dilution of the lubricant in water at a ratio of about 1:100 to about 1:500 parts of lubricant per parts of aqueous diluent and applied to conveyor surface. The continuous phase medium can comprise either an aqueous, hydrophilic or aqueous solution or composition or aqueous medium or a oleophilic, non-aqueous composition or oleophilic medium. Such materials can be applied in limited amounts directly onto a conveyor surface and can provide adequate lubricating properties at the container conveyor interface. Lubricants of the invention can comprise a transparent dispersion of an oleophilic, typically a silicone fluid, natural oil, a petroleum oil or other oleophilic materials in a hydrophilic phase such that the oil or oleophilic material has a reduced particle size of less than 300 nm, preferably less than 100 nm in the continuous hydrophilic phase. Alternatively, the dispersion can comprise small particles of a hydrophilic material dispersed in an oil phase. In such an embodiment, the hydrophilic phase can have a particle size of less than 300 nm., preferably less than 100 nm. as described above, most preferably about 1 to 80 nm. The clarity or cloudiness (turbidity) of the lubricant compositions can be measured by common spectrophotometers such as a Spectronic Genesys 5 spectrophotometer at a wavelength of about 400 nm. Other wavelengths can be used if the selected wavelength can measure the scattering of light representative of clear solutions. Other conventional particle size measuring methods can also be used. The mixtures are substantially clear with an absorption optically clear with absorption, in general, below 0.1 preferably below 0.05 measured at 400 nm. Here the absorption is defined as the fraction of incident light loss due to scattering. Other factors can impact the absorbance measured in the lubricant. Factors such as wavelength of light, the difference of refractive index between the medium and the scattering particulate, droplet or unit, the number of droplets per unit volume and the volume of the scattering units or droplet.
The invention can have a number of aspects. One aspect of the invention involves a method of use of a microemulsion lubricant of oleophilic liquid. The lubricant comprises, in a liquid aqueous medium, a dispersion of a oleophilic oil composition and optionally a lubricant additive composition. A further aspect of the invention involves contacting a conveyor and/or container with a liquid dispersion of a hydrophilic lubricant in a liquid hydrocarbon oil. In a third aspect the lubricants detailed above can be used simultaneously with a second lubricant composition.
Preferred oleophilic materials that can be used in such an environment, as the dispersed droplets in the oil-in-water emulsion or as a continuous oil phase, include oils including hydrocarbon oils, fatty oils, silicone oils, and other oleophilic oily or hydrocarbon lubricants from a variety of sources. One particularly useful form of the lubricant is the form of a silicone material that can be used in common lubricant compositions. Further, one particularly advantageous form of such lubricants is in the form of an aqueous dispersion of the silicone dispersion that is in a lubricant formulation.
In one preferred lubricant material of the invention, we have found that an effective lubricant can be made by combining a liquid diol, triol or polyol (either a liquid material or a solution of the material in an aqueous diluent) with an oleophilic material such as an oil, a silicone oil, a petroleum oil, a natural oil, dissolved or dispersed in an aqueous medium that can contain a variety of additional additive materials. We have found that close control of a weight ratio of diol, triol or polyol to water provides ability to control clarity and to obtain a transparent lubricant using commonly opaque or translucent silicone materials. For the purpose of this patent application, the term xe2x80x9copaquexe2x80x9d means that substantially all light is either reflected or scattered by a liquid mass. The term xe2x80x9ctranslucentxe2x80x9d means that some light can pass through a liquid mass, a substantial proportion of the light being reflected or scattered. Lastly, the term xe2x80x9ctransparentxe2x80x9d indicates that virtually all light passes without reflection, or scattering through a liquid mass and an observer can see through such a liquid mass under controlled conditions. A liquid may have an absorbance at a certain wavelength, but still be in a form that is visually clear. In such a clear solution, any absorbance would be a molecular absorbance. The absorbance measured in the methods of this invention relate to light scattered by the emulsion droplets of a size that efficiently scatters visible wavelengths. We have provided a means to measure the optical clarity of a liquid material using a spectrophotometric technique establishing an absorbance (the fraction of incident light loss due to scattering) that is representative of clarity or optical clarity elsewhere in the application.
For the purpose of this specification and claims, the term xe2x80x9ccoatingxe2x80x9d is intended to mean a continuous or discontinuous thin liquid layer of the lubricant dispersions of the invention on a moving conveyor surface. Such a coating can be formed by applying the liquid to the surface such that the surface of the conveyor is substantially completed covered with the lubricant. Alternatively, the term xe2x80x9ccoatingxe2x80x9d can also connote the timed application of the lubricant such that the lubricant can be applied intermittently to a surface of a moving conveyor. The intermittent application of the lubricant can still provide an adequate lubricating layer on the surface. For the lubricant to work successfully, there must be an amount of lubricant at the container conveyor interface to obtain reduced coefficient of friction. In other words, a successful lubricant coating is present when the lubricant is present at the interface to successfully reduce friction during conveying of a container from place to place on a conveyor.
A still more preferred lubricant system of the invention involves a lubricant comprising a substantial proportion of glycerin or glycerol and a minor proportion of a silicone oil dispersed in an aqueous phase that can contain emulsion stabilizing materials derived from the silicone material or added separately in the preparation of the lubricant material. The microemulsion lubricant can have a dispersed phase that can be made from a dispersion with an initial particle size that can range from about 0.3 to about 2 microns. Surprisingly, combining an opaque silicone dispersion with an initial particle size of about 0.3 to 2 microns in the lubricants of the invention can produce a clear composition with particle size of less than 300 nm thus obtaining and maintaining clarity. Major influences of the silicone emulsion component in the stability and clarity of the clear lubricant composition or microemulsion include silicone oil structure, the molecular weight of the silicone, the type of the emulsifier, emulsion concentration and particle size.
We have found that one important characteristic for maintaining a stable clear microemulsion relates to the glycerin to water ratio. We have found that for the glycerin/water/silicone microemulsion system that the glycerin and water ratio to produce and maintain a clear, transparent lubricant comprises about 2 parts per weight glycerin per each 1 part by weight of water to as little as 1 part of glycerin per each 1 part of water in the total emulsion composition.
At a certain ratio of glycerin to water, we are able to obtain a transparent beverage lubricant with ingredient(s) of silicone emulsion(s) such as:
Glycerin:Water (wt:wt ratio)=1.2 to 1.6 for Lambert silicone emulsion E2175 (60% dimethylsiloxane)
Glycerin/Water (wt:wt ratio)=1.2 to 1.6 for Lambert silicone emulsion E2140FG (35% dimethylsiloxane)
We have found that by forming microemulsion materials, the undesirable creaming or phase separation of many emulsion or macroemulsion compositions can be avoided or significantly reduced. Phase separation is undesirable in the appearance of the product and depending on the formulation can cause nozzle plugging in equipment used to manufacture and dilute the lubricants and apply the lubricants to conveyors. Lubricants have reduced viscosity in comparison to some macro emulsions that is helpful in certain applications where the materials need to be pumped through lines on small orifices. Further, we believe that microemulsions are easier to clean and can be removed with water rinses or simple surfactant cleaning practices.
The compositions of the invention can be used for lubricating food and beverage containers on many conveyor surfaces. Conveyor surfaces can include thermoplastic or thermoset polymer materials, composite, metallic or multicomponent surfaces. Containers include coated cellulosic carton, paper carton, plastic, metal and glass containers. One aspect of the invention involves thin coating lubrication of conveyor systems used in food packaging and beverage bottling and can be obtained using a continuous or discontinuous thin coating of a stable dispersion or microemulsion lubricant layer formed on a conveyor surface. The lubricant layer is maintained at a thickness of less than about 3 millimeters, preferably about 0.0001 to 2 mm, with an add on of lubricant on the surface of less than about 0.05 gms-inxe2x88x922, preferably about 5xc3x9710xe2x88x924 to 0.035 gms-inxe2x88x922, most preferably about 2xc3x9710xe2x88x924 to 0.025 gms-in xe2x88x922. Such a thin lubricating coating of the dispersed or microemulsion lubricant on the conveyor provides adequate lubrication to the conveyor system but ensures that the lubricant cannot generate high foam, does not flow from the conveyor surface and contacts the absolute minimum surface area of the food container such as the beverage bottle as possible. The form of the microemulsion can be either water-in-oil or oil-in-water methods of the invention can be used to convey virtually any food container on a conveyor line, but is particularly adapted to transporting carton container, glass bottles, steel and aluminum cans and thermoplastic beverage containers such as polycarbonate, high density and low density polyethylene, polyethylene terephthalate (PET) beverage containers. Common PET beverage containers are formed with a base cup or with a complex curvature in the base including the xe2x80x9cchampagnxe2x80x9d base, the petaloid base having a five lobed structure in the base or other shapes that provide stability to the bottle when it is placed on a surface. The contact with the lubricant on the pentaloid base must be minimized.
We have found that using a thin coating of the dispersed or microemulsion lubricant, that less than about 100 to 3000 mm2, preferably 100 to 2000 mm2 of the surface of the bottle is contacted with lubricant. Certainly, the height of the lubricant in contact with the bottle is less than 3 millimeters. The motion of the conveyor, the tendency of the bottles to rock or move while being conveyed and the other aspects of relative movement at the bottle conveyor interface affect the height of the lubricant on the bottle. The methods of this invention are primarily directed to conveyor operations and do not involve any change in shape of the container arising from forming operations. The desirable coefficient of friction of the conveyor lubricant is less than about 0.14, preferable less than about 0.1.
Another aspect of the invention provides a method for lubricating the passage of a container along a conveyor comprising applying a mixture of a dispersed or emulsified silicone material and a water-miscible lubricant to at least a portion of the container-contacting surface of the conveyor or to at least a portion of the conveyor-contacting surface of the container. The present invention provides, in another aspect, a lubricated conveyor or container, having a lubricant coating on a container-contacting surface of the conveyor or on a conveyor-contacting surface of the container, wherein the coating comprises a mixture of a water-miscible silicone material and a water-miscible lubricant. The invention also provides conveyor lubricant compositions comprising a mixture of a water-miscible silicone material and a water-miscible lubricant. During some packaging operations such as beverage container filling, the containers are sprayed with warm water in order to warm the filled containers and discourage condensation on the containers downstream from the filling station. This warm water spray can dilute the conveyor lubricant and reduce its lubricity.
The compositions used in the invention can be applied in relatively low amounts and can be formulated such that the lubricants do not require in-line dilution with significant amounts of water. The compositions of the invention provide thin, substantially non-dripping lubricating coatings. In contrast to lubricants diluted with large amounts of water, the lubricants of the invention provide drier lubrication of the conveyors and containers, drier conveyor line and working area, and reduced lubricant usage, thereby reducing waste, cleanup and disposal problems.
In another aspect of the invention, the lubricants of the invention can also be used in a conventional dilute system. The lubricant microemulsions are contacted with aqueous diluents at a ratio of about 1 part of lubricant by volume per each 100 to 500 parts of diluent. The resulting aqueous lubricant is carefully applied to a conveyor container interface to lubricate filling operations.